Preparation, assay, and partial purification of a thymic lymphocytopoietic factor (thymosin).

Abstract
A new in vitro assay for testing lymphocyto-poietic activity of thymic extracts is reported. Utilizing this assay, the preparation and partial purification of a calf thymic lymphocyto-poietic factor, for which the name thymosin is suggested, are described. The properties of the most purified fraction suggest that lymphocyto-poietic activity is associated with a relatively heat-stable carbohydrate-containing protein with a particle size less than 10,000. This product also stimulates lymphocytopoiesis when assayed in vivo. The purified product does not appear to be identical with any of the previously described preparations with lymphocytopoietic activity.